1. Field of the Invention
The present invention relates to a conductive paste capable of being baked at a low temperature and suitable, for example, for the application of forming a circuit on a glass substrate, and a glass circuit substrate suitable for the application as a defogging glass for an automobile window formed therewith.
2. Description of the Related Art
A defogging glass for an automobile window for preventing fogging caused by dew condensation having a circuit (thick film electrode) found on the surface of a glass by applying a conductive paste and generating heat by energizing the circuit (thick film electrode) has been used.
Recently, glass having the rear surface of the thick film electrode circuit colored thickly has been preferred as the defogging glass. Conventionally, the thick coloring has been obtained in the rear surface of the circuit (thick film electrode) by forming the electrode with a conductive paste containing a pigment such as a chromium (Cr) oxide.
However, even in the case of using the above-mentioned conventional conductive paste containing a pigment such as a chromium (Cr) oxide, sufficient coloring cannot always be obtained, and thus a conductive paste having a better coloring property has increasingly been desired.
Moreover, a conductive paste having a pigment such as a chromium (Cr) oxide gives rise to problems of difficulty in sintering and a low bonding strength of the thick film electrode on the glass surface.
As to the bonding strength, a method for promoting sintering by changing the sintering conditions is conceivable, such as raising the temperature at the time of sintering. However, since the glass itself comprising the circuit cannot endure high temperature, there is a limit in the sintering temperature.
To overcome the above described problems, preferred embodiments of the present invention provide a conductive paste capable of being baked at a low temperature, with sufficient coloring, and suitable for forming a circuit on a glass substrate, and a glass circuit substrate suitable for the application in a defogging glass for an automobile window formed therewith.
One preferred embodiment of the present invention provides a conductive paste comprising a conductive component, a glass frit and a vehicle, wherein: the glass frit comprises a main glass component and at least one member selected from the group consisting of alumina (Al2O3), silica (SiO2), titania (TiO2) and zirconia (ZrO2).
Since the above described conductive paste uses a glass frit prepared by adding at least one of Al2O3, SiO2, TiO2 and ZrO2 to a main glass component as the glass frit, color dimness can be prevented by restraining dispersion of Ag into the glass substrate, and thus sufficient coloring can be obtained without adding a pigment. Moreover, since a pigment needs not be added, the baking operation can be conducted at a low temperature efficiently.
In the above described conductive paste, the conductive component may comprise (a) Ag, or (b) Ag and at least one of Cu, Pd and Pt, as the main substance.
Since (a) Ag, or (b) Ag and at least one of Cu, Pd and Pt is used as the main substance comprising the conductive component, a conductive paste capable of forming an electrode having sufficient conductivity for certain can be obtained, and thus it is advantageous.
As the conductive component, a part of a metal component can be contained in a resinate state.
In the above described conductive paste, nickel (Ni) or copper oxide (CuO) may be added for adjusting the resistance. When nickel (Ni) or copper oxide (CuO) is added for adjusting the resistance, a conductive paste having a desired characteristic can be obtained by adjusting the resistance, and thus the present invention can further be effective.
In the above described conductive paste, the glass frit may be prepared by adding at least one of alumina (Al2O3) powders, silica (SiO2) powders, titania (TiO2) powders and zirconia (ZrO2) powders to at least one Pb-containing glass, Bi-containing glass, Zn-containing glass or Ba-containing glass, and adjusting the average particle size D50 in the range from about 0.5 to 2.5 xcexcm.
Since a glass frit prepared by adding at least one of Al2O3 powder, SiO2 powder, TiO2 powder or ZrO2 powder to at least one Pb-containing glass, Bi-containing glass, Zn-containing glass or Ba-containing glass, and adjusting the average particle size D50 in the range from about 0.5 to 2.5 xcexcm is used, sufficient coloring can be obtained without adding a pigment more certainly as well as the baking operation can be conducted efficiently at a low temperature.
In the above described conductive paste, powders with an about 40 to 90 m2/g specific surface area may be used for the alumina (Al2O3) powders, the titania (TiO2) powders and the zirconia (ZrO2) powders, powders with an about 150 to 300 m2/g specific surface area may be used for the silica (SiO2) powders, and at least one of the alumina (Al2O3) powders, the silica (SiO2) powders, the titania (TiO2) powders or the zirconia (ZrO2) powders may be added so as to have an about 5 to 60% by weight content ratio in the glass frit.
Then powders with an about 40 to 90 m2/g specific surface area are used for the Al2O3 powders, the TiO2 powders and the ZrO2 powders or powder with an about 150 to 300 m2/g specific surface area are used for the SiO2 powders, and at least one of the Al2O3 powders, the SiO2 powders, the TiO2 powders and the ZrO2 powders is added so as to have an about 5 to 60% by weight content ratio in the glass frit, sufficient coloring can be obtained without adding a pigment and the baking operation can be conducted efficiently at a low temperature, and thus the present invention can further be effective.
In the above described conductive paste, the glass frit may be contained in about 2.0 to 8.0% by weight ratio. At this weight ratio, a conductive paste having stable characteristics concerning sintering, bonding and coloring can be obtained.
Another preferred embodiment of the present invention provides a glass circuit substrate comprising a circuit on a glass substrate provided with the above described conductive paste.
The above described glass circuit substrate obtained by forming a circuit on a glass substrate with the conductive paste has a good coloring property and excellent bonding strength of an electrode (circuit), and thus a high reliability can be obtained.
The above described glass circuit substrate may serve as a defogging glass for an automobile window.
Since the glass circuit substrate obtained by forming a circuit on a glass substrate with the conductive paste is used as a defogging glass for an automobile window, a defogging glass for an automobile with high quality and high reliability can be provided with sufficient coloring and the excellent bonding property.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.